1. Field of the Invention
This invention relates to materials for gaskets, and more particularly to a graphite-containing gasketing material adapted for both high-temperature (e.g., greater than 1000.degree. F.) and low-temperature service applications.
2. Background Art
Numerous materials are known which are suitable for use in gaskets, for example, to provide a fluid-type seal between engaging pipes, conduit or similar confronting or mating parts. In applications such as sealing in cylinder heads of internal combustion engines, valves of high-temperature process lines and various types of machinery operating at high temperatures, gaskets are often subjected to especially severe thermal and mechanical stress in service. In general, conventional gaskets which are employed in such applications comprise a base sheet of metal or of fibrous composition which is held together by a suitable binder, and a deformable layer or bead which covers all or only selected areas of the base sheet. In service, the deformable layer, under pressure, spreads to conform to the surfaces of the mated parts between which the gasket lies, helping to achieve a desired seal between the parts.
Particularly in high-temperature and abrasive applications, the material of a gasket should be especially resistant to the severe stresses of service. The gasket material should also enable the gasket, following use, to be removed from between engaged parts without sticking thereto. Accordingly, various materials, compositions, and structural combinations have been suggested for use in gaskets. For example, U.S. Pat. No. 2,055,471 to Balfe discloses a laminated material having a fibrous, compressible layer and a layer of graphite or of a graphite mixture bonded thereto to provide non-sticking properties. Also disclosed is treatment of the graphite layer with an adhesive composition such as sodium silicate, shellac, lacquer or varnish, to form a protective skin for the laminate. In U.S. Pat. No. 3,002,850 to Fischer graphite is disclosed as a component of a low-friction sheet material. The material comprises a fabric sheet coated with a composition containing an acrylic resin and finely-divided graphite, the purpose of the coating being to minimize heat and wear from abrasive machinery parts in contact with the material. U.S. Pat. No. 3,231,460 to Andrews discloses a sheet material for gaskets which comprises fibrous asbestos impregnated with polytetrafluoroethylene, and bonded to an unimpregnated fibrous material to form a laminate. U.S. Pat. No. 4,006,881 to Gaillard discloses a fluid-type packing for closure devices. Part of the packing is composed of a sheet of carbonaceous material formed from carbon fibers and expanded graphite; the sheet is said to be compacted at least partially by compression transverse to the plane thereof.
Materials are known which are composed predominately of graphite, and which do not have a significant non-graphite fiber content. Such known materials are capable of performing satisfactorily in many gasketing applications, and of exhibiting many properties, such as temperature resistance, wear resistance and lubricity, which are normally associated with graphite. However, heretofore known materials are generally expensive, by comparison with other conventional gasketing materials, require special processing and handling procedures and do not, because of relatively low tensile strength and resistance to tearing, readily adapt to continuous production processes. A particular problem in continuous, mass production of graphite-based material is that it has not heretofore been feasible to produce large quantities of the material in sheet form on conventional equipment, for example, paper-making equipment, and then to store the material in large sheets or rolls prior to its being further processed or stamped into a desired form for the particular gasketing application.